Carrying excess weight has long been known to increase the risk of heart disease.

But overweight people with heart problems may actually live longer than their thinner counterparts, new research suggests.

U.S. researchers found the risk of heart attack and death from cardiovascular complications ishighest among underweight patients - with death rates the lowest in heavier people.

While obesity is linked to higher levels of
insulin, higher blood pressure, higher cholesterol and diabetes, the new figures suggest there is an 'obesity paradox'.

Paradox: While obesity is linked to a host of health problems such as high blood pressure and cholesterol, overweight people with heart problems may actually live longer than their thinner counterparts

One explanation may be that overweight
patients are more likely to be prescribed medication to control high blood pressure and cholesterol levels than slimmer people - and in higher doses.

They are also more likely to undergo procedures such as bypass surgery - and traditionally been considered to have a worse recovery rate because of their size.

But research is increasingly suggesting that a higher BMI protects against death from many diseases - despite the fact it may help trigger them in the first place.

The new study, published in the journal Mayo Clinic Proceedings, sought to re-examine assumptions about body fat and explore this 'obesity paradox'.

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Led by Dr
Abhishek Sharma, of the State University of New York, it analysed 36 previous studies involving tens of thousands of patients with coronary artery disease.

Those with a low BMI - defined as less than 20 - had between a 1.8- to 2.7-fold higher risk of
heart attack and death from heart problems.

Conversely, the risk of death from cardiovascular complications was lowest
among overweight patients with a high BMI (25-30) compared to people
with a normal BMI (20-25).

But it was severely obese people who fared the best, according to the study.

The death rate in those with a BMI in the 30-35
and over-35 range was up to 27 per cent lower than those with a normal BMI.

'At this stage, we can only speculate on the reasons for this paradox,' said Dr Sharma.

Unexpected: The more overweight a person was, the lower their risk of death from heart problems, the research found

'One explanation may be that overweight
patients are more likely to be prescribed cardio-protective medications
such as beta blockers and statins and in higher doses than the normal
weight population.'

These people may also have what's known as a higher'metabolic reserve' - i.e. their hearts are better able to cope with increases in workload.

Dr Sharma added: 'Obese and overweight patients
have been found to have large coronary vessel damage, which might
contribute to more favorable outcomes [than those who have smaller damaged vessels].

Commenting on the study, obesity expert Dr Kamyar Kalantar-Zadeh, of the University of California Irvine Medical Centre, said: 'Although the underlying mechanisms of the obesity paradox remain unclear, the consistency of the data is remarkable.